A. Field of the Invention
The present invention relates to improvements in vibration drivers for feeding and orienting parts of components into automatic assembly systems or similar uses.
B. Description of the Prior Art
In general, vibratory feeders employ a small amplitude vibration in the path or track along which parts travel. The direction of such vibrations, in order to be effective in advancing the parts along the track, must be at an appropriate angle with respect to the direction of the force of gravity acting on the parts. For example, with the vibration of the track set at 45 degrees, with respect to the direction of gravitational force (upward to the right and downward to the left), the parts in the track will move to the right. A change of 90.degree. in the vibration angle causes the parts to move to the left along the track.
Progressive motion of the parts along the track may be explained as follows. On the rising part of the vibration cycle, the parts press against the track by the force of gravity plus the inertial force from the acceleration of the mass of the part. This tends to keep the parts moving with the track. However, on the descending half of the vibration cycle, the pressure of the parts against the track due to the gravitational force is reduced by the residual, upward momentum of the part already acquired and, in addition, the track is moving downward away from the part. Thus, the part has little or no force against the track during the downward portion of the vibration cycle. In effect, the track moves downward and under the parts then picks them up and advances them on the next upward half-cycle to the right or left depending upon the direction of the vibration angle.
Prior art vibratory parts feeders employ a track member having mass (M.sub.1) and a relatively heavy base (M.sub.2) generally 5 to 10 times the mass of the track member. The track member and base are coupled together by means of a plurality of angularly disposed, flat springs. Typically, an electromagnetic actuator is connected between the track and base so as to cause the track to move upward to the right and downward to the left or visa versa, as required.
If alternating current or current pluses at a definite frequency are applied to the actuator, the track and base will vibrate toward and away from each other at twice the frequency of the alternating current, or at the pluse frequency if D.C. pulses are used. Such a structure will exhibit mechanical resonance at a specific frequency determined by the mass of the track, the mass of the base and the effective rate of the spring system. This relation is expressed as follows: ##EQU1## where:
n is the natural frequency of the system,
K equals the effective spring rate,
M.sub.1 equals the mass of track,
M.sub.2 equals the mass of the base.
The amplitude of vibration of each mass in such a two-mass system is inversely proportional to the mass. Thus, if the mass of the base is ten times the mass of the track, the amplitude of the track vibrations will be approximately ten times that of the base.
In practice, such vibration systems are applied to linear, circular or helical tracks. In the case of circular or helical tracks, for example the track element, is coupled to the relatively heavy base member by three or more flat springs arranged symmetrically around the periphery of the track at an appropriate angle with respect to the direction of the gravitational force. The electromagnetic drive element is arranged to deflect the system against the combined spring force. The motion of the track is necessarily helical, downward clockwise and upward counterclockwise or visa versa depending upon the angle of the mounting springs. The parts will proceed along the track in the direction of the upward half of the vibration cycle.